Cellulose insulation fibers are commonly used as insulation fibers and these are defined, for example, in Japanese Industrial Standards (JIS) A-9523:2001. Cellulose insulation fibers are fluff-like material obtained by cracking a raw material, such as used newspapers or corrugated boards, and then processing the cracked material through a fibrillator. The cellulose insulation fibers have excellent heat-insulation and sound-absorption properties because of millions of air chambers in each fiber itself and air contained between intertangled fibers. For the purpose of using as a building material, there has heretofore been known a dry blowing method in which the cellulose insulation fibers are blown directly onto the inner surface of the roof or the wall surface of a building to form a deposit of the cellulose insulation fibers.
However, the cellulose insulation fiber deposit formed through the dry blowing method is be undesirably involved in a so-called settling-down phenomenon in which the top of the deposit will settle down with time, and the height of the deposit can be eventually reduced by about 15 to 20% of its initial height. In particular, if cellulose insulation fibers are deposited on a vertical wall surface through the dry blowing method, the settling-down becomes obvious to cause a gap between the top of the deposit and the building structure initially in contact with the deposit, resulting in significantly deteriorated heat-insulation, anti-condensation and sound-insulation performances. Further, existing celluros fibers can be actually handled only by specialized agencies, because the celluros fibers are formed in a sort of fluffs and thereby it is inconveniently required to surround the work environment with an anti-scattering cover such as a plastic sheet during the blowing operation of cellulose insulation fibers on a vertical surface of a wall or the like.